Valve distributor piston assembly for high pressure pump

ABSTRACT

An improved valve distributor piston assembly for a high pressure fluid pump includes a rigid inner and resilient outer member, both mounted for reciprocation between front and rear stop plates at the end of a reciprocating piston rod. The inner piston element is configured to maximize operating life of the outer piston element by reducing its exposed frontal area, and to stabilize the reciprocating motion of the piston assembly with respect to the pump rod and the pump cylinder.

Unite States Patent Brenneman 51 Feb. 18,1975

[ VALVE DISTRIBUTOR PISTON ASSEMBLY FOR HIGH PRESSURE PUMP [75] Inventor: Homer K. Brenneman, Delphi, Ind. [73] Assignee: Bremco Industries, Lafayette, Ind. [22] Filed: Feb. 19, 1974 [21] Appl. N0.: 443,693

[52] U.S. Cl. 417/51] [51] Int. Cl. F04b 7/00 [58] Field of Search 417/510, 511, 512, 513

[56] References Cited UNITED STATES PATENTS l,376,863 5/1921 Drew 4l7/5ll l,4l4,808 5/l922 Fiese 5/l96l Hanje 4l7/5ll Primary Examiner-William L. Freeh Assistant Examiner-Gregory Paul LaPointe Attorney, Agent, or Firm-Bacon & Thomas [57] ABSTRACT An improved valve distributor piston assembly for a high pressure fluid pump includes a rigid inner and resilient outer member, both mounted for reciprocation between front and rear stop plates at the end of a reciprocating piston rod. The inner piston element is configured to maximize operating life of the outer piston element by reducing its exposed frontal area, and to stabilize the reciprocating motion of the piston assembly with respect to the pump rod and the pump cylinder.

3 Claims, 5 Drawing Figures Uchiyama 417/51 1 BACKGROUND OF THE INVENTION High pressure pumps of the type described in US. Pat. No. 3,558,244 Uchiyama utilize a floating" distributor piston at the end of a reciprocating piston rod. The piston is a two-part assembly including an inner, rigid piston element, and a resilient cup-like outer element which supports the piston in the pump cylinder between spaced stop plates mounted at the end of the piston rod, and enables the piston assembly to be selfcentering in the cylinder.

The front stop plate is apertured, and, during operation, pumped fluid is drawn from the supply inlet side of the pump to the expanding outlet pumping chamber through the distributor piston assembly and the apertured plate during the back-stroke of the piston rod. On the front-stroke, the piston assembly slides to a sealing position, preventing pumped fluid from bypassing the piston unit, and the fluid in the front pumping chamber is urged out of the pumping cylinder under the positive influence of the piston assembly.

The present inventor has observed a high failure rate of piston assemblies constructed in accordance with certain prior art configurations at elevated temperature pressure conditions when using pumps of the type discussed above. The discovery was made that certain forms of prior art pistons were rocking on the end of the piston rod under extreme operating conditions, that the resilient outer piston element was failing due to high temperature/pressure effects on the exposed large frontal area of the element, causing the element to blow" out of position on the inner piston element, and that the lack of stability at the piston area had a contributory effect on unstabilized lateral motions of the piston rod of the pump unit.

The present invention is an improved configuration for a piston assembly in a pump unit of the type described that eliminates or minimizes the deficiencies observed, and provides a piston assembly having dem onstrated longer life and stability during operation of the pump at elevated temperature/pressure conditions.

SUMMARY OF THE INVENTION The present invention relates to an improved distributor piston assembly for use in a pump unit described above. The distinctive characteristics of this piston include an inner piston element that is axially longer than the spacing between front and rear piston stop plates, with closely controlled radial clearances between the various piston and stop plate elements and between the inner piston and the pumping cylinder. An improved resilient outer piston element design is also incorporated in the invention, whereby the exposed frontal area of the outer piston element is minimized and the operating movements of the piston assembly are stabilized.

The outer piston element to cylinder wall friction forces are reduced by the improved design and the operating life of piston assemblies constructed in accordance with the present invention has been observed as being remarkably improved over the prior art designs, particularly under more extreme operating conditions.

DESCRIPTION OF THE DRAWINGS In the attached drawings:

FIG. 1 shows a partial sectional view of a portion of a valved piston for a high pressure pump made in accordance with the prior art;

FIG. 2 shows a partial cutaway elevational view of the piston embodying the present invention in a pump assembly;

FIG. 3 shows a sectional elevational view of the inner portion of the piston embodying the present invention;

FIG. 4 shows a sectional elevational view of the outer centering and sealing ring portion of the piston embodying this invention; and

FIG. 5 shows a detail view of a portion of the assembled piston embodying the present invention.

With reference to the drawing, FIG. 1 shows the arrangement of the piston assembly of the high pressure pump constructed in accordance with the prior art. Inner piston element 1, usually constructed of metal, has a circumferential undercut 2 which provides a seat for outer piston sealing and centering ring 3 which is made of a suitable elastomeric material.

The piston assembly then is seen to comprise the inner metal ring element 1 and the outer seal element -3. Its orientation and relative placement in a pump system is shown in the above-mentioned US. Pat. No. 3,558,244, and the detailed description thereof and of the pump with which it is intended to be used is incorporated herein by reference. Suffice it to note here that, as shown in that patent and as shown in FIG. 2 of this disclosure, piston assemblies of this type are selfcentering units, and perform a valving-(distribution) function with respect to fluids pumped by the apparatus with which they are associated.

The frictional properties of the outer seal elements, the relative motions of the piston elements and the piston rods, the fluid forces acting on the piston assembly, all combine in a very simple and efficient manner to cause reciprocation of the piston assembly with respect to front and rear piston stop plates or discs to cause fluid to be pumped from an inlet side supply to an out let side under high pressure. The pumps are short stroke, of course, and operate at a frequency range depending on the specific requirements of a particular pump.

As can be further noted in FIG. 1, the outer piston element 3 frictionally engages the cylinder wall 4, and is usually circumferentially compressed when the piston assembly is installed in the cylinder of the pump.

The piston assembly 1, 3 of FIG. 1 needs to perform as a piston only on the forward or pumping stroke of the pump in which it is incorporated. This pumping stroke would be towards the left, as viewed in FIG. 1. On the reverse back-stroke, or inlet stroke, fluids to be pumped bypass the piston assembly through a central port area, defined in part by the inner cylindrical wall 5 of piston l. Fluids pass to the outlet side of the piston assembly through this port area, and, on the pumping stroke, the port is automatically closed off by the inner piston element, and the outer resilient seal member blocks the passage of fluid being pumped past the piston assembly. The seal element 3 acts in part as a cupseal and is urged outwardly against the cylinder wall by fluid pressure acting on the front face 6 of the element 3. The seal element 3 is provided, therefore, with a relatively large frontal area to enhance the sealing properties of the element, and necessarily is of a relatively massive construction to achieve proper sealing, resiliency, and to provide energy absorption and damping of transverse piston motion during operation of the pump.

It should be remembered that the piston assembly in effect floats" on the piston rod, and the outer seal ring 3 of the prior art assembly serves as the transverse centering means for the piston assembly in the cylinder.

The present invention is based on the discovery that, as compared with typical piston assemblies of the prior art, a remarkable improvement in piston life and pump performance is obtained by utilizing a piston configured as shown in FIGS. 2 through 5, which are described in detail below.

The valved piston assembly of the present invention comprises an inner piston element 7 shown in detail in FIG. 3 and an outer seal and centering element 8, shown in detail in FIG. 4.

In FIG. 2, the piston assembly is shown in its relative position in a high pressure pump with which it is intended for use. The relevant pump details include a piston rod 9 having a reduced section 10 at its distal end which threadably receives a suitable fastener 11 held in place by a lock element 12. Lock washer 12a may comprise a part of the fastener assembly.

The reduced diameter 10 is separated from the major body portion 9 of the piston rod by a shoulder 13. Fixedly retained on rod 9 intermediatethe fastener 11 and shoulder 13 are a solid rear piston stop plate 14, a cylindrical spacer element 15, and an apertured forward piston stop plate 16. The stop plates 14 and 16 preferably are circular shaped, as is the cylinder 17 of the pump assembly. Multiple apertures 18 of suitable size extend through the forward stop plate 16 for reasons which will be obvious as the present description proceeds.

The front stop plate 18, as seen in FIG. 5, includes a generally planar rear stop surface l8r and the rear stop plate 14 includes a front piston stop surface 14f. Piston assembly 7, 8 can be readily seen to fit between the front and rear stop plates between surfaces l8r and 14f when the pump unit is assembled, with the exception of a front portion of the inner piston element 7, which will be described below.

The inner piston element 7 comprises, as best seen in FIG. 3, a main rear body portion 19 and a forward portion 20. The rear portion 19 includes an axially extending inner cylindrical wall surface of diameter D and a conical tapered section 22 extending between cylindrical wall 21 and forward stop wall surface 23 of piston element 7. The stop wall 23 defines the rearward end of forward section which is generally cylindrical in form, has a forward end face 24 and a thickness comprising the difference between inner and outer diameters D D respectively, of section 20.

The circumferential area of rear portion 19 of piston element 7 includes a channel cutout 27 for receiving the outer piston element 8 in a close-fitting relationship. Stepped surface 28 extends between the circumferential surface 26 of front piston portion 20 and the forward sidewall 29 of the channel 27 and the rear sidewall 30 thereof. The rear stop surface 31 of piston element 7 defines the rearward end face or extremity of the preferred inner piston element here described. Obviously, this is a stop surface and need not be the rearward extremity of an inner piston element having a different form than what is shown in the drawings.

Outer piston element 8 is resilient, formed from a suitable elastomeric material, and is initially shaped in its relaxed condition as shown in FIG. 4. It is generally cylindrical in form, having an inner cylindrical wall 32, an outer wall 33, a forward end surface 34 and a rearward end surface 35.

The inner and outer walls 32 and 33 are initially parallel tapered by an amount T which may be in the order of four degrees. The outer wall 33 is inwardly stepped at 36.

The outer piston seal and centering element 8 is installed into channel 27 of inner piston element 7 by slightly stretching the element 8 and snapping it into the channel area. Front and rear walls 34, 35 are then proximate front and rear sidewalls 29, 30 of channel 27, as seen in FIG. 5. The taper T is eliminated when the piston assembly is placed in cylinder 17 of the pump unit, and the taper is converted to a torsional stress in element 8 which is somewhat relieved after a few hours of operation at elevated temperatures. The assembly then appears as shown in FIG. 2, with the piston assembly 7, 8 held centered in cylinder 17 by the outer resilient piston section 8 and located between stop plates 14 and 16 by inner piston element 7. The relative dimensions of the piston and disc assembly of FIG. 2 is important to the realization of the present invention. The outer diameter (O.D.) of front stop plate 16 must, of course, be less than the inner diameter (I.D.) of cylinder 17 of the pump unit. Moreover, the inner diameter D of front portion 20 of piston section 7 is larger than the CD. of plate 16 so as to leave a small clearance 36a (FIG. 5) between these members. The outer diameter D, of piston portion 20 is likewise slightly smaller than the diameter of cylinder 17 so as to leave a clearance between the inner piston element 7 and the cylinder 17. The overall length L of piston element 7 is greater than the distance between plate stop surfaces l8r and l4f(FIG. 5), while the length L of the element 7 between its stop surfaces 23 and 31 is smaller than the distance between plate stop surfaces l8r and 14f. Thus, when the rearward stop surface 31 of piston element 7 abutts the forward stop surface of rear stop plate 14, at least a portion of the forward section 20 of piston element 7 extends between the front stop plate 16 and the cylinder 17, as shown in FIG. 2.

With further reference to FIG. 2, the operation of the high pressure pump unit incorporating the valved piston assembly embodying this invention can be visualized. The pump unit has a supply fluid inlet end 37 and a high pressure outlet end 38 for pumped fluid. A crank (not shown) rotated by a suitable power drive means to the right of FIG. 2 causes rectilinear reciprocation of piston rod 9. The rod 9 is moving in the direction of the arrow in FIG. 9, and is carrying out a pumping stroke.

In this mode, fluid trapped to the left of the piston assembly is forced from the area in front of the forwardly travelling piston unit, and prevented from rearwardly bypassing the piston unit due to the outer seal provided by resilient piston element 8 and the face to face contact between rear stop surface 31 of element 7 and front stop 14f of plate 14. Leakage between other elements mounted on the piston rod in the area of the piston assembly is minimal and normally is tolerated.

On the reverse, or intake stroke of rod 9, the piston assembly 7, 8 is to the left as viewed in FIGS. 2 and 5,

with stop face 23 abutting rear stop surface l8r of plate 16. Movement of rod 9 is to the right, and fluid to the right, or inlet side, of piston assembly 7, 8 moves around the outer edge of rear plate 14, through the central cylindrical section 21 of piston element 7, and through the apertures 18 in front plate 16 to fill up the increasing volume to the left of piston assembly 7, 8 in cylinder 17. Of course, suitable check valves are provided in the inlet and outlet sections of the high pressure pump unit of FIG. 2, but such details are not within the scope of the present invention.

The advantages of the present inventive concept can be readily understood and appreciated by considering the following. The piston unit of the present invention reduces markedly the frontal area of the resilient sealing and centering element 8 that is exposed to high temperature/pressure fluids being pumped, thus increasing its life under such operating conditions. This further reduces its susceptibility to deterioration from other operating conditions, including the tendency of the outer resilient element to blow out of the channel 27 or to extrude itself between the cylinder 17 and piston element 7 at high pressure operating conditions.

The rod 9 has a high front end loading and is stabilized by the piston assembly 7, 8 at its forward or working end. The increased length of the solid piston element 7, including the extension of the forward section 20 over the forward stop plate tends to further stabilize the travel of rod 9, as well as to stabliize the vibrational characteristics of the piston assembly 7, 8 during operation of the pump.

The small clearance area 36a and the smaller clearance around the inner piston element 7 between its outer surfaces and the cylinder 17 become filled with pumped fluid, providing a further front and rear stabilizing effect on the piston assembly, and minimizing the tendency of piston element 7 to twist and scuff the cylinder wall 17.

The clearances are sufficient, of course, to enable pumped fluid pressure to act on the forward face 34 (FIG. 4) of piston element 8 to enable enhancement of its sealing characteristics by longitudinal compression and radial expansion of the elastomeric material of which element 8 is formed.

A typical piston assembly comprises an inner piston 7 approximately 0.5 in. in overall length between front and rear extreme surfaces 24, 31. The element 7 is about 0.78 in. overall diameter (D and the channel 27 is about 0.21 in. long and approximately 0.08 in. deep. It is thus seen that the axial length of the ouer piston element 8 is in the order of one half the length of the piston assembly in this embodiment.

The inner diameter of cylinder 17 is approximately 0.8 in., so that the clearance between the inner piston 7 and cylinder'l7 is in the order of approximately 0.01 in. The thickness of the rear portion 19 between the inner diameter D, and outer diameter D is approximately 0.16 in. deep, so that it can be seen that the channel depth is about one half of the total thickness of rear portion 19. The installed inner piston normally represents about 82 percent volume area of the cylinder.

The result ofthis design is the procurement ofa stabilized reciprocating motion of the piston assembly 7, 8

The foregoing is a description of a preferred embodiment of this invention, and is provided as an exemplary disclosure only, not to be construed as limiting the scope ofthe invention beyond what is recited in the following claims.

I claim:

1. In a high pressure pump having a reciprocating piston rod, a cylinder having an internal diamete r, forward and rear stop plates fixedly mounted in spaced apart relationship on said rod, said plates having outside diameters less than said cylindrical internal diameter, said forward stop plate being apertured and having a generally radially extending rear piston stop surface, and said rearward stop plate having a generally radially extending forward piston stop surface; an improved piston assembly mountedon said rod for slidable motion in said cylinder between said plates, comprising:

a. an inner rigid piston element having forward and rear body portions,

l. said rear body portion including inner front and rear generally radially extending stop surfaces axially spaced apart a distance less than the distance between said stop plates;

2. said rear body portion also having an inner diameter less than the diameter of said stop plates between the said inner piston front and rear stop surfaces;

3. said inner piston further having a forward portion extending forwardly of said piston front stop surface;

4. said inner piston forward portion extending between the outer diameter of said forward stop plate and said cylinder internal diameter when said inner piston rear stop surface abuts said rearward stop plate forward stop surface;

5. said inner piston forward portion also having an internal diameter slightly greater than said outer diameter of said forward stop plate and an outside diameter slightly less than said cylindrical internal diameter;

6. said rear body portion of said inner piston having an outer circumferential channel;

b. an outer piston element mounted in said inner pis' ton channel, said outer piston element being resilient, and extending between said channel and said cylinder in a compressed state to effect piston sealing and centering functions during operation of said pump.

2. The improved piston assembly recited in claim 1, further wherein said pump includes a cylindrical spacer element extending coaxially with said piston rod be tween said front and rear stop plates, and wherein said inner diameter of said inner piston rear body portion is greater than the outside diameter of said cylindrical spacer element to provide a flow circuit between said inner piston and said spacer.

3. The improved piston assembly as recited in claim 2, further wherein the axial length of said channel is approximately one half the total length of said inner pis- 

1. In a high pressure pump having a reciprocating piston rod, a cylinder having an internal diameter, forward and rear stop plates fixedly mounted in spaced apart relationship on said rod, said plates having outside diameters less than said cylindrical internal diameter, said forward stop plate being apertured and having a generally radially extending rear piston stop surface, and said rearward stop plate having a generally radially extending forward piston stop surface; an improved piston assembly mounted on said rod for slidable motion in said cylinder between said plates, comprising: a. an inner rigid piston element having forward and rear body portions,
 1. said rear body portion including inner front and rear generally radially extending stop surfaces axially spaced apart a distance less than the distance between said stop plates;
 2. said rear body portion also having an inner diameter less than the diameter of said stop plates between the said inner piston front and rear stop surfaces;
 3. said inner piston further having a forward portion extending forwardly of said piston front stop surface;
 4. said inner piston forward portion extending between the outer diameter of said forward stop plate and said cylinder internal diameter when said inner piston rear stop surface abuts said rearward stop plate forward stop surface;
 5. said inner piston forward portion also having an internal diameter slightly greater than said outer diameter of said forward stop plate and an outside diameter slightly less than Said cylindrical internal diameter;
 6. said rear body portion of said inner piston having an outer circumferential channel; b. an outer piston element mounted in said inner piston channel, said outer piston element being resilient, and extending between said channel and said cylinder in a compressed state to effect piston sealing and centering functions during operation of said pump.
 2. The improved piston assembly recited in claim 1, further wherein said pump includes a cylindrical spacer element extending coaxially with said piston rod between said front and rear stop plates, and wherein said inner diameter of said inner piston rear body portion is greater than the outside diameter of said cylindrical spacer element to provide a flow circuit between said inner piston and said spacer.
 2. said rear body portion also having an inner diameter less than the diameter of said stop plates between the said inner piston front and rear stop surfaces;
 3. said inner piston further having a forward portion extending forwardly of said piston front stop surface;
 3. The improved piston assembly as recited in claim 2, further wherein the axial length of said channel is approximately one half the total length of said inner piston element.
 4. said inner piston forward portion extending between the outer diameter of said forward stop plate and said cylinder internal diameter when said inner piston rear stop surface abuts said rearward stop plate forward stop surface;
 5. said inner piston forward portion also having an internal diameter slightly greater than said outer diameter of said forward stop plate and an outside diameter slightly less than Said cylindrical internal diameter;
 6. said rear body portion of said inner piston having an outer circumferential channel; b. an outer piston element mounted in said inner piston channel, said outer piston element being resilient, and extending between said channel and said cylinder in a compressed state to effect piston sealing and centering functions during operation of said pump. 